Southern Pamir Research Articles

Mesozoic tectonics of the Gondwanan terranes of the Pamir plateau

The Central and Southern Pamir terranes represent Gondwanan crustal fragments within the Pamir plateau, and are bounded by the Tanymas, Rushan–Pshart, and Wakhan-TBZ suture zones from north to south. Stratigraphic and geochronologic data suggest that collision of the Central and Southern Pamir terranes with the southern margin of Asia was broadly coeval during the latest Triassic–earliest Jurassic Cimmerian orogeny (∼200Ma). The Cimmerian orogeny in the Pamir region does not appear to have resulted in significant crustal thickening of the Central and Southern Pamir as both terranes are overlain by Lower to Middle Jurassic carbonate platform deposits. Post-suturing latest Triassic–earliest Jurassic sandstones with a strong arc signature in the Southern Pamir suggest derivation from the Karakul–Mazar terrane to the north, implying the Northern Pamir were a region of elevated topography relative to the Gondwanan terranes immediately after closure of the Palaeotethys and Rushan ocean basins.A key question in the post-Cimmerian tectonic evolution of the Pamir is the extent and magnitude of Mesozoic deformation of the Central and Southern Pamir. Three lines of evidence suggest that much of the post-Jurassic crustal shortening documented in the Central and Southern Pamir is related to Mesozoic tectonic activity, rather than the Cenozoic India–Asia collision as generally interpreted: (1) The Southern Pamir does not record post-Jurassic marine deposition indicating the terrane elevated above sea level by the Early Cretaceous, most likely due to crustal shortening and thickening; (2) Coarse terrigenous deposits distributed throughout the Central and Southern Pamir interpreted to be syn-tectonic with regional folding and thrust faulting are poorly dated with many studies interpreting them to be Jurassic to Cretaceous rather than Paleogene; (3) Strong Cretaceous crustal thickening and shortening documented to the south in the Karakoram terrane, and to the north in the Northern Pamir, suggest that the Central and Southern Pamir were similarly affected. These relationships suggest that most of the upper crustal shortening documented in the Central and Southern Pamir is related to retroarc deformation north of the Jurassic–Cretaceous Andean margin that developed within the Karakoram and Southern Pamir terranes during subduction of the Neotethys Ocean. Thus, the Pamir plateau may have been a westward continuation of the pre-Cenozoic “Lhasa-plano” of the Tibetan plateau.

Present‐day deformation of northern Pakistan from Salt Ranges to Karakorum Ranges

AbstractEpisodic GPS measurements are used to quantify the present‐day velocity field in the northwestern Himalaya from the southern Pamir to the Himalayan foreland. We report large postseismic displacements following the 2005 Kashmir earthquake and several mm/yr thrusting of the central segment of the Salt Ranges and Potwar Plateau over the foreland, westward thrusting of Nanga Parbat above the Kohistan Plateau, and ~12 mm/yr SSE velocities of the Karakorum Ranges and of the Deosai and Kohistan Plateaus relative to the Indian Plate. Numerical simulations allow to determine a first approximation of slip along active faults: (1) substantial creep of ~87 mm/yr between 2006 and 2012 along the flat northeast of the Balakot‐Bagh Thrust affected by the 2005 earthquake; (2) ~5 mm/yr slip of the central segment of the Salt Ranges and Potwar Plateau, whereas their western boundaries are clearly inactive over the time span covered by our measurements; (3) 13 mm/yr ductile slip along the Main Himalayan Thrust modeled by a dislocation dipping 7° northward, locked at a depth of 15 km; and (4) ~20 mm/yr slip along the shear zone forming the western boundary of Nanga Parbat, between depths of 1.6 and 6.5 km. Residuals velocities suggest the existence of left‐lateral strike slip along the Jhelum Fault.

Unexpected finding of the invasive Baikalian amphipodGmelinoides fasciatusin a cold spring of the southern Pamir Mountains

A specimen of the Baikalian micruropodid amphipod Gmelinoides fasciatus was recently found in a spring brook in the Shugnansky District, Gorno-Badakhshan Autonomous Province of Tajikistan. This occurrence represents the first record confirmed with mt-cox1 sequence data for this species from the Pamir Mountains. Reliable information on the introduction of Gm. fasciatus and the pattern of its distribution in the region is not yet available, but we hypothesise that the species was introduced intentionally to increase the fish productivity of Yashilkul Lake in 1973−1974. This finding of probably an isolated population shifts the southernmost limit of the species range approximately 1400 km from the Bukhtarminskoye reservoir, Eastern Kazakhstan. A general overview of the morphology, ecology, distribution and invasive history of the species is provided.

A late Pleistocene glacial chronology from the Kitschi-Kurumdu Valley, Tien Shan (Kyrgyzstan), based on 10Be surface exposure dating

Surface exposure dating has become a helpful tool for establishing numeric glacial chronologies, particularly in arid high-mountain regions where radiocarbon dating is challenging due to limited availability of organic material. This study presents 13 new 10Be surface exposure ages from the Kitschi-Kurumdu Valley in the At Bashi Range, Tien Shan. Three moraines were dated to ~15, 21 and >56ka, respectively, and corroborate previous findings that glacial extents in the Tien Shan during Marine Oxygen Isotope Stage (MIS) 2 were limited compared to MIS 4. This likely documents increasingly arid conditions in Central Asia during the last glacial cycle. Morphological evidence in the Kitschi-Kurumdu Valley and a detailed review of existing numeric glacial chronologies from the Tien Shan indicate that remnants of the penultimate glaciation (MIS 6) are preserved, whereas evidence for MIS 5 glacier advances remains equivocal. Reviewed and recalculated exposure ages from the Pamir mountains, on the other hand, reveal extensive MIS 5 glacial extents that may indicate increased monsoonal precipitation. The preservation of MIS 3 moraines in the Tien Shan and the southern Pamir does not require any monsoonal influence and can be explained alternatively with increased precipitation via the westerlies.

A Probabilistic Assessment of Earthquake Hazard Parameters in NW Himalaya and the Adjoining Regions

The maximum likelihood estimation method is applied to study the geographical distribution of earthquake hazard parameters and seismicity in 28 seismogenic source zones of NW Himalaya and the adjoining regions. For this purpose, we have prepared a reliable, homogeneous and complete earthquake catalogue during the period 1500–2010. The technique used here allows the data to contain either historical or instrumental era or even a combination of the both. In this study, the earthquake hazard parameters, which include maximum regional magnitude (M max), mean seismic activity rate (λ), the parameter b (or β = b/log e) of Gutenberg–Richter (G–R) frequency-magnitude relationship, the return periods of earthquakes with a certain threshold magnitude along with their probabilities of occurrences have been calculated using only instrumental earthquake data during the period 1900–2010. The uncertainties in magnitude have been also taken into consideration during the calculation of hazard parameters. The earthquake hazard in the whole NW Himalaya region has been calculated in 28 seismogenic source zones delineated on the basis of seismicity level, tectonics and focal mechanism. The annual probability of exceedance of earthquake (activity rate) of certain magnitude is also calculated for all seismogenic source zones. The obtained earthquake hazard parameters were geographically distributed in all 28 seismogenic source zones to analyze the spatial variation of localized seismicity parameters. It is observed that seismic hazard level is high in Quetta-Kirthar-Sulaiman region in Pakistan, Hindukush-Pamir Himalaya region and Uttarkashi-Chamoli region in Himalayan Frontal Thrust belt. The source zones that are expected to have maximum regional magnitude (M max) of more than 8.0 are Quetta, southern Pamir, Caucasus and Kashmir-Himanchal Pradesh which have experienced such magnitude of earthquakes in the past. It is observed that seismic hazard level varies spatially from one zone to another which suggests that the examined regions have high crustal heterogeneity and seismotectonic complexity.

The tectonometamorphic evolution of the Alpine metamorphic belt of the Central Pamir

Himalayan Journal of Sciences Vol.2(4) Special Issue 2004 pp. 131

Trace elements and evolution of granite melt as exemplified by the Raumid Pluton, Southern Pamirs

New trace element data were obtained by ICP-MS for 58 samples representing eight intrusive phases of the Raumid granite Pluton. All of the rocks, except for one sample that was deliberately taken from a greisenized zone, were not affected by postmagmatic fluid alteration. The sequential accumulation of incompatible trace elements (Rb, Ta, Nb, Pb, U, and others) in the Raumid Pluton from the early to late phases coupled with a decrease in incompatible element contents (Sr, Eu, Ba, and others) indicates a genetic link between the granites of all phases via fractional crystallization of a granite melt. The REE distribution patterns of final granite phases are typical of rare-metal granites. The Ta content in the granites of phase 8 is only slightly lower than that of typical rare-metal granites. Greisenization disturbed the systematic variations in trace element distribution formed during the magmatic stage. The ranges of trace element contents (Rb, Sr, Ta, Nb, and others) and ratios (Rb/Sr, La/Lu, Eu/Eu*, and others) in the Raumid granite overlap almost entirely the ranges of granitic rocks of various compositions, from the least differentiated with ordinary trace element contents to rare-metal granites. This indicates that the geochemical signature of rare-metal granites can develop at the magmatic stage owing to fractional crystallization of melts, which is the case for the melt of the Raumid granite.

Near-Ultrahigh Pressure Processing of Continental Crust: Miocene Crustal Xenoliths from the Pamir

Xenoliths of subducted crustal origin hosted by Miocene ultrapotassic igneous rocks in the southern Pamir provide important new information regarding the geological processes accompanying tectonism during the Indo-Eurasian collision. Four types have been studied: sanidine eclogites (omphacite, garnet, sanidine, quartz, biotite, kyanite), felsic granulites (garnet, quartz, sanidine and kyanite), basaltic eclogites (omphacite and garnet), and a glimmerite (biotite, clinopyroxene and sanidine). Apatite, rutile and carbonate are the most abundant minor phases. Hydrous phases (biotite and phengite in felsic granulites and basaltic eclogites, amphiboles in mafic and sanidine eclogites) and plagioclase form minor inclusions in garnet or kyanite. Solid-phase thermobarometry reveals recrystallization at mainly ultrahigh temperatures of 1000–1100 C and nearultrahigh pressures of 2 5–2 8GPa. Textures, parageneses and mineral compositions suggest derivation of the xenoliths from subducted basaltic, tonalitic and pelitic crust that experienced highpressure dehydration melting, K-rich metasomatism, and solid-state re-equilibration. The timing of these processes is constrained by zircon ages from the xenoliths and Ar/Ar ages of the host volcanic rocks to 57–11Ma. These xenoliths reveal that deeply subducted crust may undergo extensive dehydration-driven partial melting, density-driven differentiation and disaggregation, and sequestration within the mantle. These processes may also contribute to the alkaline volcanism observed in continent-collision zones.

Assembly of the Pamirs: Age and origin of magmatic belts from the southern Tien Shan to the southern Pamirs and their relation to Tibet

Magmatic rocks and depositional setting of associated volcaniclastic strata along a north‐south traverse spanning the southern Tien Shan and eastern Pamirs of Kyrgyzstan and Tajikistan constrain the tectonics of the Pamirs and Tibet. The northern Pamirs and northwestern Tibet contain the north facing Kunlun suture, the south facing Jinsha suture, and the intervening Carboniferous to Triassic Karakul–Mazar subduction accretion system; the latter is correlated with the Songpan‐Garze–Hoh Xi system of Tibet. The Kunlun arc is a composite early Paleozoic to late Paleozoic‐Triassic arc. Arc formation in the Pamirs is characterized by ∼370–320 Ma volcanism that probably continued until the Triassic. The cryptic Tanymas suture of the southern northern Pamirs is part of the Jinsha suture. A massive ∼≤227 Ma batholith stitches the Karakul–Mazar complex in the Pamirs. There are striking similarities between the Qiangtang block in the Pamirs and Tibet. Like Tibet, the regional structure of the Pamirs is an anticlinorium that includes the Muskol and Sares domes. Like Tibet, the metamorphic rocks in these domes are equivalents to the Karakul–Mazar–Songpan‐Garze system. Granitoids intruding the Qiangtang block yield ∼200–230 Ma ages in the Pamirs and in central Tibet. The stratigraphy of the eastern Pshart area in the Pamirs is similar to the Bangong‐Nujiang suture zone in the Amdo region of eastern central Tibet, but a Triassic ocean basin sequence is preserved in the Pamirs. Arc‐type granitoids that intruded into the eastern Pshart oceanic‐basin–arc sequence (∼190–160 Ma) and granitoids that cut the southern Qiangtang block (∼170–160 Ma) constitute the Rushan‐Pshart arc. Cretaceous plutons that intruded the central and southern Pamirs record a long‐lasting magmatic history. Their zircons and those from late Miocene xenoliths show that the most distinct magmatic events were Cambro‐Ordovician (∼410–575 Ma), Triassic (∼210–250 Ma; likely due to subduction along the Jinsha suture), Middle Jurassic (∼147–195 Ma; subduction along Rushan‐Pshart suture), and mainly Cretaceous. Middle and Late Cretaceous magmatism may reflect arc activity in Asia prior to the accretion of the Karakoram block and flat‐slab subduction along the Shyok suture north of the Kohistan‐Ladakh arc, respectively. Before India and Asia collided, the Pamir region from the Indus‐Yarlung to the Jinsha suture was an Andean‐style plate margin. Our analysis suggests a relatively simple crustal structure for the Pamirs and Tibet. From the Kunlun arc in the north to the southern Qiangtang block in the south the Pamirs and Tibet likely have a dominantly sedimentary crust, characterized by Karakul–Mazar–Songpan‐Garze accretionary wedge rocks. The crust south of the southern Qiangtang block is likely of granodioritic composition, reflecting long‐lived subduction, arc formation, and Cretaceous‐Cenozoic underthrusting.

Palaeomagnetic investigation in the Pamirs and its tectonic implications

This paper presents a palaeomagnetic investigation in the Pamirs of Tadjikistan. Remanences are mainly carried by magnetite and are of secondary, synfolding origin. Application of a new method, the small-circle reconstruction, allows to extract palaeomagnetic rotation and tectonic tilting since the time of remanence acquisition (assumed to be ∼20 Ma). In some regions consistent rotations are observed: (i) clockwise in the Muzkol area of the central Pamirs; (ii) following the trend of oroclinal bending in the northern Pamirs; and (iii) counterclockwise in the northern folded sequence of the southern Pamirs. However, variations within different regions are obvious and scattering even occurs within smaller areas. Most likely, local block rotations are caused by N–S shortening. Palaeomagnetic and tectonic results reveal that tilt axes are rotated around vertical axes in the course of progressive shortening/folding. Surprisingly, the scatter of the tilt axes is reduced hereby. By comparing the distributions of the present and former tilt axes the amount of shortening is estimated for the southern Pamirs (shortened to ∼40%) and the central Pamirs (shortened to ∼60%).

Quaternary deformation in the Eastern Pamirs, Tadzhikistan and Kyrgyzstan

Active deformation in the eastern Pamir of Central Asia is concentrated on the margins of the orogen with minor deformation within the high terrain. Along the Trans‐Alai mountain front at the northern perimeter of the orogen, Quaternary thrusting is documented by uplifted pediments, now at >500 m above the piedmont, Holocene fault scarps, and large earthquakes with N to NW oriented P axes. Seismicity in the interior of the orogen outlines a N–S belt that includes normal faulting events with E–W oriented T axes. N–S striking, active normal faults in the interior Lake Karakul region are compatible with these earthquakes; they define an asymmetric graben with a master fault at the western basin margin. In the southern Pamirs, dextral strike‐slip faults root in the dextral Karakorum Fault, which bounds the Pamirs to the east. A mixture of dextral and reverse offsets totalling 135 m in Pleistocene terraces and 8 m in late Pleistocene/Holocene deposits demonstrates contemporary transpression, indicating average displacement rates of <1 mm/yr. The concentration of young thrusts along the Trans‐Alai, the northward migration of thrusting, and the scarcity of other large‐scale shortening features within the eastern Pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihilation of the intermontane Alai Valley. Widespread dextral shear in the eastern Pamirs, both to the south and north of the extensional Karakul depression, and combined dextral strike‐slip and normal faulting in the Muji‐Tashgorgan graben of the Chinese Pamirs are interpreted as localized space accommodation phenomena, formed during progressive transfer of compressional deformation along a dextral strike‐slip deformation zone with extensional stepovers.

Structure of the lithosphere along the deep seismic sounding profile: Tien Shan—Pamirs—Karakorum—Himalayas

During 1973–1977, as part of the International Geodynamic Project, some seismic investigations of the Earth's crust have been carried out by geotraverses of the Tien Shan—Pamirs—Karakorum—Himalayas. The seismic data obtained together with other geophysical information, allow the construction and interpretation of the lithospheric section through the Pamirs-Himalayas structure. This section includes thick crust with complex layering, supra-asthenospheric and asthenospheric layers of the upper mantle. The thickness of the Earth's crust increases from 50–55 km in the north, in the Ferghana depression (Tien Shan), to 70–75 km in the south, near the Karakul Lake (Northern Pamir). It varies within 60–65 km for the Central and Southern Pamir, Karakorum and the Inner Himalayas. Its thickness is least (35–37 km) in the south, under the outer margin of the Himalayan foredeep. Extreme gravity minima and depressions on the geoid surface correspond to the regions with maximum thickness of the Earth's crust. The centers of the disturbing masses on the geoid surface are located in the vicinity of the asthenosphere's upper layer; this determines the effect of the whole lithospheric layer, including its asthenospheric layer, at intense changes of gravity anomalies. The asthenospheric upper layer is recorded at a depth of about 120 km, its base at a depth of 200 km, in the northern and southern regions, and 300 km in its central part (Southern Pamir, Karakorum). In the middle asthenospheric layer, wave velocities decrease to 7.5 km/sec, under the base they increase to 8.4 km/sec and reach 9.4 km/sec at a depth of about 400 km. In the supra-asthenospheric layer of the upper mantle, longitudinal and shear wave-velocities slightly increase (by less than 0.1 km/sec) towards its base.

Ophiolite obduction and geologic evolution of the Oman Mountains and adjacent areas

Structural and stratigraphic relationships in the Oman Mountains developed by Late Cretaceous collision between the northern passive margin of the African continent and an island arc. Field relationships and metamorphic facies indicate that ophiolite obduction was accomplished by continental underthrusting of the fore-arc limb of an island-arc edifice at considerable depth. Uplift of the ophiolite slab resulted from both compressional shortening and isostatic interaction of the continental crust with the mantle rock it underthrust. This model may apply to many other major ophiolite areas of the world, specifically Newfoundland, Cuba, northern Venezuela, Cyprus, the Urals, eastern Celebes, New Guinea, and New Caledonia. Events preceding the Mesozoic convergence of Africa and Eurasia and resultant Oman collision include late Paleozoic rifting in the present Turkey-Iran area, which produced a microcontinent comprising the Menderes and Kirsehir massifs of Turkey and the Rezaiyeh-Esfandagheh belt of Iran, separated from Eurasia by a northerly arm of the Tethys and from Africa by a southerly arm of the Tethys. Central Iran and central Afghanistan–southern Pamir–Karakorum are believed to have been a part of Gondwana positioned between Somalia and India. They too were affected by late Paleozoic rifting but did not reach their present position until early Tertiary time, driven north along with India by sea-floor spreading of anomaly 28 time and later.

Certain laws governing development of mobile belt in central and mountainous Asia

The tectonic evolution of a large, complex, mobile region in Central and mountainous Asia is summarized and documented from early Paleozoic to Middle Tertiary. Four basic stages are recognized: the epi-Proterozoic platform, the geosyncline, the young platform, and the activated platform. Generally, the timing coincides with late Precambrian, middle-late Paleozoic, middle-late Mesozoic, and Cenozoic, respectively. Each of these stages started and finished at different times in different parts of the composite mobile belt. The sedimentary, volcanic, and orogenic record is summarized and interrelated in the northern Tien-Shan, Central Tien-Shan, southern Tien-Shan, Kun-Lun and northern Pamir, southern Pamir and Karakorum, and Himalayan provinces. — L.T. Grose.